The present invention relates to a tapered roller bearing, and more particularly, to a tapered roller bearing which is arranged in a final reduction gear of an automotive vehicle, etc. and is lubricated using oil accommodated in the final reduction gear, and a bearing device for supporting a pinion shaft, which supports the pinion shaft using two inclined contact type rolling bearings disposed in a housing.
A tapered roller bearing which is provided with an outer race, an inner race, a plurality of tapered rollers interposed between the outer race and the inner race, and a cage for retaining the tapered rollers has been widely used since it is compact, stands large radial and axial loads and is suitable for high speed rotation. However, when compared to a ball bearing, the tapered roller bearing suffers from a larger torque loss. Therefore, in view of energy utilization efficiency, it is necessary to decrease a torque loss of the tapered roller bearing.
Referring to FIG. 7, a related tapered roller bearing 21 includes an outer race 22, an inner race 23, a plurality of tapered rollers 24 interposed between the outer race 22 and the inner race 23, and a cage 25 for retaining the tapered rollers 24. A small-diameter end portion of the cage 25 is bent radially inward to form a bent portion 25a. The bent portion 25a is positioned opposite to a small flange portion 23a of the inner race 23 with a predetermined clearance defined between the bent portion 25a and the small flange portion 23a. 
In Japanese Patent Laid-Open No. 10-89353, there is disclosed a tapered roller bearing which is formed in consideration of the clearance defined between the bent portion of the cage and the small flange portion of the inner race.
In the related tapered roller bearing shown in FIG. 7, by a pumping action resulting from the rotation of the tapered roller bearing, lubricant oil is introduced from a small diameter side of the inner race into the tapered roller bearing and discharged from the tapered roller bearing through a large diameter side of the inner race. Resistance between the tapered rollers and the inner race and resistance by agitation of the lubricant oil serve as factors for generating a rotational torque. In particular, in the case of a tapered roller bearing which is used at a high rotational speed, the resistance by agitation of the lubricant oil occupies a large part of the rotational torque.
In the tapered roller bearing disclosed in Japanese Patent Laid-Open No. 10-89353, a separation phenomenon of the bearing is prevented by considering the flow of lubricant oil. Nevertheless, in this type of tapered roller bearing, it is necessary to control the clearance between the bent portion of the cage and the outer surface of the inner race so that the bent portion of the cage is not brought into contact with the inner race while the inner race rotates, and therefore, only a narrow tolerance range is allowed in the manufacture of the tapered roller bearing.
Next, a differential mounted on a vehicle such as an automobile will be described below. In a differential of a vehicle, a pinion shaft is supported by two tapered roller bearings in a housing (for example, see Japanese Patent Laid-Open No. 11-48805). In the two tapered roller bearings, since contact areas among the outer race, the tapered rollers and the inner race are substantial and the tapered rollers slide on a large flange portion of the inner race, large rotational resistance is induced. In this regard, although the two tapered roller bearings are lubricated by an oil bath lubrication method in which lubricant oil accommodated in the housing is forced to be introduced into the tapered roller bearings, if an excessive amount of lubricant oil is introduced into the tapered roller bearings, as agitation resistance of the lubricant oil increases, rotation resistance also increases. Further, as abrasion debris from gears, etc. which is contained in the lubricant oil enters the tapered roller bearings, the tapered rollers and raceways of the outer and inner races are likely to be damaged.